1. Field of the Invention
The present invention relates to draft gears and, in particular, to an improved friction/elastomeric pad draft gear having an extended travel for the absorption and dissipation of input forces.
2. Prior Art
Coupler systems for modern railroad cars typically have included a draft gear assembly to cushion and absorb forces placed on the system during car operation. Devices to cushion and absorb such forces may comprise an elastomeric spring package coupled with a frictional restraint device.
Examples of such devices are exemplified by U.S. Pat. Nos. 4,556,149 and 4,591,059 both of which are assigned to the assignee of the present invention and incorporated by reference herein.
While such draft gear devices have high shock absorbing capacities they tend to transmit a high magnitude of force to the car structure during a work cycle.
The present invention overcomes the disabilities of the prior art by providing a friction/elastomeric pad draft gear which absorbs energy over a longer distance of travel than prior art devices thereby enabling the transmission of lower levels of force to the rail car structure when cushioning a given energy input. In accordance with friction/elastomeric pad draft gears, the present invention includes a housing with a closed end and an open opposite end which is provided with an extended tapered internal friction surface. A wedge is mounted for axial movement in the open end of the housing and is situated for direct application of draft or buff forces. Friction devices or stepped friction shoes are positioned within the housing, between the wedge and the extended tapered internal friction surface to absorb some of the shock created by the application of a force to the wedge. A spring seat is positioned between the friction devices and the elastomeric pad stack. The stepped friction shoes cooperate with the spring seat to increase the available space for the elastomeric pad stack. A guide spike is secured to the closed end of the housing and passes through the elastomeric pad stack, spring seat and wedge to lessen the potential of buckling of the pad column.
The friction devices of this invention include a series of annularly spaced friction shoes each having a first, flat beveled inner surface in engagement with a flat beveled inner surface of the wedge. The beveled inner surfaces are formed at a first selected angle with respect to the major axis of the housing. Each of the friction shoes also has a second flat, beveled outer face in engagement with the extended tapered internal friction surface, located in the open end of the housing, forming a second selected angle with the major axis of the housing. Each of the friction shoes also has a third flat, inner face in engagement with a flat, outer face formed in the spring seat, the third flat inner face of the shoe and the outer face of the spring seat being formed at a third selected angle with respect to the major axis of the housing. The guide spike is held stationary at all times as a result of the head of the spike being kept tight against the rear wall of the housing by virtue of the preload to which the elastomeric pad is subjected. A pilot hole through the center of the spring seat and through the center of the wedge enables inward displacement of the wedge and spring seat while maintaining the spike""s central alignment.
In the preferred embodiment of the invention, the first selected angle of the adjoining surfaces of the friction shoe and the wedge is approximately 35 degrees plus or minus about 3 degrees. The second selected angle of the adjoining surfaces of the friction shoe and the extended tapered internal friction surface is approximately 2.25 degrees plus or minus about 0.25 degrees. The third selected angle of the adjoining surfaces of the friction shoe and the spring seat surface is approximately 90 degrees plus or minus about 4 degrees. The elastomeric pad stack comprises a plurality of concentric springs which are made in accordance with U.S. Pat. Nos. 4,198,037 and 4,566,678 which are incorporated by reference herein.
Thus, an object of this invention is the provision of a draft gear wherein the available travel to installed length ratio is about 0.21. The ratio of the available travel to the installed length of modern draft gears has heretofore ranged from about 0.11 to about 0.16 with the vast majority having a ratio of about 0.14.
Still a further object of the invention is to provide a draft gear which employs friction/elastomeric devices, fits in a standard pocket, and has 120 mm of travel. This extent of travel having been possible heretofore only with expensive hydraulic draft gears.
An additional, object of this invention is to provide a draft gear for application in a standard pocket which has 120 mm of travel, weighs less and can absorb more energy than a conventional draft gear.
Another object of this invention is to provide a stepped friction shoe in combination with a spring seat whereby allowing a longer elastomeric spring column to be located within the draft gear housing.